Three-dimensional temporomandibular joint muscle attachment morphometry and its impacts on musculoskeletal modeling

Abstract

In musculoskeletal models of the human temporomandibular joint (TMJ), muscles are typically represented by force vectors that connect approximate muscle origin and insertion centroids (centroid-to-centroid force vectors). This simplification assumes equivalent moment arms and muscle lengths for all fibers within a muscle even with complex geometry and may result in inaccurate estimations of muscle force and joint loading. The objectives of this study were to quantify the three-dimensional (3D) human TMJ muscle attachment morphometry and examine its impact on TMJ mechanics. 3D muscle attachment surfaces of temporalis, masseter, lateral pterygoid, and medial pterygoid muscles of human cadaveric heads were generated by co-registering measured attachment boundaries with underlying skull models created from cone-beam computerized tomography (CBCT) images. A bounding box technique was used to quantify 3D muscle attachment size, shape, location, and orientation. Musculoskeletal models of the mandible were then developed and validated to assess the impact of 3D muscle attachment morphometry on joint loading during jaw maximal open-close. The 3D morphometry revealed that muscle lengths and moment arms of temporalis and masseter muscles varied substantially among muscle fibers. The values calculated from the centroid-to-centroid model were significantly different from those calculated using the 'Distributed model', which considered crucial 3D muscle attachment morphometry. Consequently, joint loading was underestimated by more than 50% in the centroid-to-centroid model. Therefore, it is necessary to consider 3D muscle attachment morphometry, especially for muscles with broad attachments, in TMJ musculoskeletal models to precisely quantify the joint mechanical environment critical for understanding TMJ function and mechanobiology.

Evaluating the morphological features of the lateral pterygoid insertion into the medial surface of the condylar process

“…However, the insertion areas evaluated in the present study were 2.0 cm 2 and were therefore larger than those of the aforementioned study. Since the insertion area on the pterygoid fovea in the present study was 1.4 cm 2 and almost identical with the study of She et al (2018), the discrepancy might be explained by whether or not there was specific focus on the insertion area on the medial surface of the condylar process. On the basis of occupying one‐third of the total insertion area, we concluded that the lateral pterygoid had a broad insertion area on the medial surface of the condylar process which should not be ignored.…”

“…Data on the dimensions of the insertion area of the lateral pterygoid is limited in the literature. Recently, She et al (2018) reported that the total insertion area of the lateral pterygoid was 1.4 cm 2 based on the three‐dimensional cone‐beam CT images. However, the insertion areas evaluated in the present study were 2.0 cm 2 and were therefore larger than those of the aforementioned study.…”

Signs and Symptoms of Temporomandibular Disorder in Male Narghile Smokers versus Male Cigarette Smokers.

“…Indeed, during the act of narghile smoking, the mandible is found to be pulled forward (personal observation). Over activity of the jaw muscles causes excessive loading of the TMJ [34]. It had been reported that overloading of the TMJ tends to squeeze the intra-articular disc forward; and with repeated activity the disc becomes permanently displaced forward at rest, leading to internal derangement of the joint [35].…”